Conventionally, as for a surface light emitter, a usage as a display has been mainstream as can be seen in a backlight light source device of a liquid crystal display device.
In recent years, a movement of using this surface light emitter as a gobo for building material and amusement etc. has been increasing. In such a case, the gobo is required to act as a transparent plate at the time when a light source is turned off, and to act as a gobo by plate-surface transversal radiant emitted light at the time when the light source is on, so as to act to block view in the back.
As for past general liquid crystal displays, in the case of a transmissive liquid crystal, a non-transparent backlight device is required and in the case of a reflective liquid crystal, a reflective plate is practically required. Therefore, in either of the case, it has been non-transparent as the whole display device.
In the surface light emitter, a configuration, in which a scattering function is incorporated by convexo-concave, dot printing, or the like to the light guide surface as can be seen in the backlight light source device of the liquid crystal display device (Patent literature 1), or a configuration, in which light diffusing particles with a small refractive index difference Δn between a refractive index of a substrate and the refractive index of the light diffusion particles are included inside (Patent literature 2), are known. In these configurations, the light guide may be opaque or a haze value in the thickness direction of the light guide is large when the light source is turned off. Therefore, although it is possible to perform shading effect when the light source is turned off, it has been difficult to act as a transparent plate at the time of extinction.